The head of the ASTI says if safety measures are not in place when re-opening schools, teachers will not be going back.
The plan is expected to be announced later on Monday, after details were discussed by Government over the weekend.
Enhanced cleaning regimes, investment in school buildings and more substitute teachers are just some of the measures planned.
But ASTI President Deirdre MacDonald told Newstalk Breakfast the measures need to be the right ones.
"We know that these are the things we have sought, we have fought a valiant battle to make sure that our members and our students will be returning to a safe environment.
"So we do hope what is necessary will be put in place, if it's not well we won't be back.
"The students won't be back, because it would not be safe.
"So whatever has to happen has to happen in line with the public health advice."
"I am very hopeful because we have laid it out extremely clearly to them that those are the parameters that we will work within.
"Now we want to get back to school - teaching is always a difficult job, but I can tell you it has been a much more difficult job when we've been trying to do it remotely.
"Our members have done huge, huge work in supporting the students - as best can be done remotely.
"So we do want to go back, but we want to go back safely.
"And the other thing, and this is very, very important, is that it must be sustainable.
"We can't have this for two or three months, because... as we move into the normal flu season, shall we say, there will be undoubtedly absence.
"We went into work with colds, flus, all sorts of bits and pieces and worked through it and that was fine.
"That can't happen [now] - if you have any raised temperature, any sniffle, any bit of a sore throat you can't take the chance.
"Those are the rules and rightly so, so you'll obviously have to be substituted".
She said that aspect will be "certainly one of the big elements, that and the monies for cleaning and the monies for adaption of the school infrastructure.
"We don't know how much will be needed, but you know that it needs to be adequate and we know it needs to be sustainable".
